Conventionally, the helper piston is applied to the plunger piston during the assist phase of braking in such a way that the plunger piston pulls the control rod and the brake pedal. Advance of the plunger piston triggers the assist operation so that it no longer presses against the reaction disk.
Under normal conditions, this advance is not noticed by the driver because his action on the brake pedal initiates the braking operation. When he releases the pressure, the pedal returns to its neutral position. If an obstacle is found beneath the brake pedal, for example, an object that has fallen and accidentally lands beneath the brake pedal, the driver notices this resistance and corrects the situation.
In the case of autonomous braking, assisted braking is triggered by the brake system management unit without the driver pressing on the brake pedal, which is drawn by the plunger piston throughout the action. This provides a haptic signal for the driver if his foot is on the brake pedal. But if the driver's foot or an obstacle is present beneath the brake pedal, there is a risk that the foot may be crushed or injured. If the obstacle is resistant, given that brake assistance is continuous, there is a risk of damaging the components of the braking system, such as the electric motor, which, while being powered, is prevented from rotating.